(1) Field of the Invention
This invention relates to a method for preventing the deposition of scale in subterranean formations or in well fluid-gathering metal equipment exposed to high temperature aqueous media. More particularly the invention relates to such a method for preventing the deposition of scale onto formation rock or metal surfaces from high temperature brines or geothermal fluids containing calcium and other scale-forming ions during production of such fluids from a subterranean formation via a well and the subsequent utilization of the produced fluid.
(2) Description of the Prior Art
Brine is often produced from subterranean formations, as through wells primarily intended for production of oil. If the well penetrates a deep subterranean formation, the brine and oil produced will be at an elevated temperature.
One source of recoverable natural energy is geothermal energy stored in hot subterranean formations. One way of utilizing this geothermal energy involves drilling one or more wells into a subterranean formation which may contain either a geothermal fluid or hot dry rocks. If it contains a geothermal fluid, the fluid may be produced via a well. If it contains only hot dry rocks, a relatively low temperature heat exchange fluid is passed through the formation and recovered via a well after it has been heated by the rocks. In either instance, the process involves, in part, the production of geothermal fluids from the formation to the surface via a well and subsequent handling of the fluid to utilize the geothermal energy. Such utilization may involve electric power generation by using the geothermal energy to drive a turbine, passing the fluid through a helical rotary screw expander power system, use in a binary power cycle with a working fluid such as isobutane in a regenerative heat exchanger, or direct utilization for its heat, water or minerals content, for space heating or process heating.
Within the formation, brine and geothermal fluids are at high temperatures and pressures. Under such conditions, these aqueous liquids characteristically contain considerable amounts of various dissolved salts. The production and subsequent utilization of these fluids involve passing them through the formation to a well and then through metal conduits and other fluid handling equipment. During this time, the fluid cools and the pressure is reduced. When this change in condition occurs, the dissolved salts tend to precipitate, adhere to the solid rock or metal surfaces with which they come in contact, and build up in thickness so as to eventually cause plugging of the formation and/or the fluid handling equipment and/or a reduction in the heat transfer properties of the system.
A wide variety of materials have been proposed for addition to hot aqueous fluids to inhibit scale formation as the fluids cool. However, more effective scale inhibitors are still desired.
It is known from U.S. Pat. No. 2,599,342 issued June 3, 1952 to Victor G. Meadors to add primary, secondary and tertiary aliphatic and cycloaliphatic amines having up to 15 carbon atoms, such as piperidine, diethyl amine and diethanol amine, to aqueous base drilling fluid as thickening agents. It is also known from U.S. Pat. No. 2,603,598 issued July 15, 1952 to Victor G. Meadors to add an alkanol amine, i.e., a mono-, di- or trihydroxy amine having not more than 15 carbon atoms to an aqueous base drilling fluid to overcome the adverse effect of calcium and magnesium salts on the fluid loss properties of the drilling fluid. U.S. Pat. No. 2,331,280 issued Oct. 12, 1943 to Truman B. Wayne describes, as an additive to reduce the viscosity of an aqueous base drilling fluid, an ester of a strong water-soluble polybasic acid, such as polybasic phosphoric acid, a hydrophile-polyhydroxy body, such as a polyhydroxy-carboxylic acid, and a strongly basic amine, such as an alkyl, cycloalkyl, alkylated or arylated amine. None of these references are concerned with inhibition of scale formation, hot brine or geothermal fluids.
Accordingly, a principal object of this invention is to provide a method for inhibiting the formation of scale from hot brine and geothermal fluids during their production from subterranean formations and subsequent handling.
Another object of the invention is to provide such a method for inhibiting the formation of a calcium-containing scale onto the metal surfaces of aqueous fluid production and fluid handling equipment.
A further object of the invention is to provide such a method for inhibiting the formation of scale from liquid-containing geothermal fluids having temperatures above about 400.degree. F.
It is a still further object of the invention to provide such a method for inhibiting the deposition of scale from high temperature wet steam.
Other objects, advantages and features will become apparent from the following description and appended claims.